O'Fallon, MO Fence Regulations: Retaining Walls (2026)

275 requires a permit for any retaining wall taller than forty-eight inches (measured from the top of the base to the top of the wall), or for any wall that supports a surcharge load or alters the channelized drainage of a lot or drainage area; permitted walls need as-built plans prepared by a certified licensed engineer when the Engineering Department requires it. Walls must be spaced from other retaining walls following a geotechnical engineer's recommendation or a minimum ratio of two feet horizontal for every one foot of vertical wall height.

In the front yard, a retaining wall cannot exceed four feet in height and must sit back at least ten feet from the front property line or outside the utility easement, whichever is greater, though the Planning and Zoning Commission or Board of Adjustment can vary that standard. Side and rear yard walls cannot be built within two feet of the property line, and any side or rear wall over forty-eight inches is barred from public utility easements entirely. A wall can exceed four feet only if a licensed engineer designs and engineers it, but no wall, regardless of engineering, may exceed six feet without a fence or guard on top.

Any wall over thirty inches that supports a walking surface within two feet of the wall needs a guard built to the current International Building Code or International Residential Code. Walls are barred from public rights-of-way without written City Engineer approval, and any wall that alters channelized drainage needs Engineering Department approval and a permit regardless of its height.